Stabilities and Coordination Modes of α-Alaninephosphonic Acid in Copper(II) Heteroligand Complexes with Ethylenediamine, Diethylenetriamine or N,N,N′,N′,N"=Pentamethyldiethylene Triamine in Aqueous Solution

Solution equilibrium studies on Cu2+-L-1-L-2 ternary systems have been performed by pH-potentiometry, UV-Vis spectrophotometry and EPR methods (L-1 corresponds to polyamines such as ethylenediamine (en), diethylenetriamine (dien), or N,N,N',N',N ''-pentamethyldiethylenetriamine (Me(5)dien) and L-2 represents 1-aminoethylphosphonic acid (alpha-alaninephosphonic acid)). The obtained results suggest the formation of heteroligand complexes with [Cu(L-1)(alpha-Ala(P))] stoichiometry in all studied systems. Additionally, in the system with en the [Cu(en)(alpha-Ala(P))H-1](-) species is formed in basic solution. Our spectroscopic results indicate tetragonal geometry for the [Cu(en)(alpha-Ala(P))] species, geometry slightly deviated from square pyramidal for the [Cu(dien)(alpha-Ala(P))] complex and strongly deviated from square pyramidal towards trigonal bipyramidal for the [Cu(Me(5)dien)(alpha-Ala(P))] species. The coordination modes in these heteroligand complexes are discussed.